<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <title>程序员常用样式</title>
  <style>
    .mydiv{
      width:300px;
      height:300px;
      background-color: blue;
      color:white;
      margin:0 auto;
      text-align: center;
    }

    .uname {
      width:420px;
      height:35px;
      border-radius: 5px;
      /*边框宽度1像素、实线、红色边框*/
      /* border:1px solid red; */
      border:2px dotted #299E59;
      background-color: azure;
    }
  </style>
</head>
<body>
<h1>背景样式</h1>
<div class="mydiv">
  今天天气不错！
</div>
<input type="text" style="background-color: red;"/>

<h1>边框样式</h1>
用户名<input type="text" class="uname">
</body>
</html>